Retention in clinical HIV care has been widely recognized as a key component in improving HIV disease outcomes in individuals and decreasing HIV transmission in populations. Measures of retention in clinical care have varied depending on the available data and the population under study, and various demographic, clinical, and environmental characteristics have been observed influencing patterns of care over time. Recently, the National HIV/AIDS Strategy (NHAS) for the United States advocated improvement in clinical retention rates and the Institute of Medicine outlined measures for assessing both the NHAS and benchmarks in the Affordable Care Act. This research therefore seeks to quantify clinical, sociodemographic, and geographic patterns and correlates of retention in care among HIV-infected persons in the United States (US) and Canada, with a particular focus on individuals with a history of injection drug use (IDU). The North American AIDS Cohort Collaboration on Research and Design (NA-ACCORD) provides a rich data source that has been endorsed by the Institute of Medicine as an important resource capable of monitoring patterns of care among persons living with HIV/AIDS in the United States and assessing progress in the NHAS. Aim 1 will quantify the concordance of laboratory measures (used as surrogates for direct measures of clinical encounters) with actual clinical encounters between 2000 and 2010. Because laboratory measures are widely used as indicators of access to clinical care, this analysis will be of significant importance and has not been previously addressed. Aim 2 will identify the effectiveness of applied interventions to improve clinical retention among HIV-infected individuals in clinical care in North America over the first decade of the 2000s. Aim 3 will identify factors associated with suboptimal retention in care, between 2000 and 2010: demographic and clinical characteristics after adjusting for time-varying confounding by immune status and substance abuse using causal inference modeling, and geographic characteristics using spatial statistics. Secondary analyses will be performed in each aim to assess the patterns and correlates of care specific to HIV-infected individuals with a history of injection drug use, noted in the NHAS and elsewhere as a population of particular interest in addressing HIV treatment and outcome disparities and effectively implementing novel strategies for reducing HIV transmission.